The fire held steady overnight at nearly 200 square miles, but a spokesman for the California Department of Forestry and Fire Protection said firefighters didn’t get their usual reprieve from cooler early morning temperatures Saturday.

“This morning we are starting to see fire activity pick up earlier than it has the last several days,” said Cal Fire spokesman Daniel Berlant. “Typically, it doesn’t really heat up until early afternoon. We could continue to see this fire burn very rapidly today.”

The Rim Fire started in a remote canyon of the Stanislaus National Forest a week ago and is just 5 percent contained. More than 5,500 homes are threatened, four have been destroyed and voluntary and mandatory evacuations are underway.

The fire has grown so large and is burning dry timber and brush with such ferocity that it has created its own weather pattern, making it difficult to predict in which direction it will move.

“As the smoke column builds up it breaks down and collapses inside of itself, sending downdrafts and gusts that can go in any direction,” Berlant said. “There’s a lot of potential for this one to continue to grow.”

After burning for nearly a week on the edges of Yosemite, the fire moved into the northwest boundary of the park Friday.

The tourist mecca of Yosemite Valley, the part of the park known around the world for such sights as the Half Dome and El Capitan rock formations and waterfalls, remained open, clear of smoke and free from other signs of the fire that remained about 20 miles away.

Dry fuel and hot weather have combined already to make this the 16th largest fire in California’s history. More than 2,600 firefighters and a half dozen aircraft are battling the blaze.

This has been a particularly busy fire season in California and throughout the West because a lack of winter rains and snow have left forests extremely dry. This year so far the U.S. Department of Forestry have fought 5,700 fires, compared with 4,900 by this date last year.